1. Brief Description of the Invention
This invention relates to anti-abrasion additives for ink formulations, also sometimes called anti-rub, slip and mar resistant ink additives. Such additives are chemicals mixed or dispersed into printing ink formulations in order to impart to such inks resistant strength and anti rub properties after printing has occurred. Ink print on paper and other materials will then resist abrasion and deterioration of the ink while maintaining slip properties, defined below, when the ink is subjected to a wide variety of smear, smudge and mar forces, including frictional forces such as packing, shipping and handling.
2. Description of the Prior Art
It is desirable for printing ink to have strength properties, so that after printing on paper or another substrate, the ink does not ruboff when the surface is subjected to abrasive forces. Inks, specifically heat-set inks, have long been formulated with special additives, designed to provide these properties, which are added by the ink manufacturer. The printing ink, as modified, will possess as well improved mar resistance. Marring of ink detracts from the perfection of readability of the word message the print is intend to convey. The ink, after addition of these special additives, also will have improved slip properties. Slip properties permit, for example, other printed pages to glide easily over the ink without causing it to wear or smudge.
Anti-abrasion additives can be added into ink formulations during manufacture by being mixed, or less preferably ground, into the formulation with the ink colors or pigments, or added as a part of the final ink blend. Such additives can also be dispersed into the precursor ink solvents or resins.
Many anti-abrasion ink additives in commercial use today are in hard wax-like solid or powder form. Anti-rub additives are generally prepared and have been often used as such in this physical form. Harder waxes have proved difficult to mix satisfactorily or disperse into ink systems as additives. The dispersion of these hard wax products into magazine inks and other similar resin-based systems is particularly burdensome. It is often required to melt the wax additive by electric or other type of heating as part of making the final printing ink. The anti-abrasion or rub qualities imparted by commercial waxes can be highly influenced by the melting temperature of a particular wax. Such waxes added to inks often result in only a small reduction in rub-off, not its complete elimination. With the heat and movement imparted by the friction of constant rubbing, particles of the ink film often continue to spread to unprinted areas. In view of these difficulties, anti-abrasion ink additives have been disfavored, and have not reached their full market potential.
The introduction of anti-abrasion hard waxes into inks in order to solve the rub-off problem, however, has introduced other problems. Often, the more wax additive that is added to improve rub resistance, the more significant the decrease in desirable gloss of the printed ink from the gloss, as printed, to a lower level, which is particularly unsatisfactory for quality magazines or prints. It is very important to a publisher to minimize this reduction in gloss of a printed ink because of abrasion forcer. Accordingly, in most applications a compromise has to be achieved between the desired level of anti-rub properties and the amount of gloss reduction.
In addition, since such anti-abrasion waxes are either solids or in powder form, they are often difficult to disperse into inks, which are essentially liquid systems. Ink manufacturers have long searched for a pumpable liquid (including near-liquid or paste-like) anti-abrasion additive, for ease of ink manufacture alone. Problems associated with the use of harder waxy additives include poor dispersibility when added to inks, and undesirably long dissolution times. An additive which requires heating, as do most hard wax anti-abrasion additive products, also presents additional manufacturing costs and problems which ink manufacturers would prefer to avoid. Finally, there is the factor of increased cost associated with an ink containing relatively expensive waxes. In the case of newspaper and certain magazine news inks, cost is an important factor and, therefore, at the present time most news inks do not ordinarily utilize anti-abrasion additives, and inexpensive magazine inks use only limited varieties and in small amounts.
Synthetic waxes such as polyethylene waxes are some types of anti-abrasion waxes used in the ink industry as anti-rub additives. Such hard waxes are often added by the ink manufacturer in the form of dispersions of the wax in resins of the same particular type characteristic of the ink formulations into which they are to be incorporated. Hard waxes prepared with polytetrafluoroethylene are known and used in a variety of printing inks in the same manner, but are especially targeted for heatset inks, where the temperature of the drying apparatus does not cause them to significantly soften or melt. Polytetrafluoroethylene-based powder waxes are also added directly to in-process inks using high shear forces imparted by fairly complicated equipment.
The incorporation of many commercial anti-abrasion waxes presents similar conventional handling problems as are encountered with the dispersion of other types of solid or nearly-solid materials. When added to ink systems, these types of waxes tend to agglomerate into clumps. When dispersed directly, there has been an "uneven wetting out" of the product resulting in the formation of lumps or globules whose core is still the dry wax. Agglomeration can be reduced in many cases by adding the wax to the system slowly, with agitation. However, such slow dissolution can affect the efficiency of specific ink manufacturing operations.
Non-pourable waxes have also proved particularly difficult to incorporate in industrial ink-making processes because they often require long periods of time to dissolve. Both in simple ink resin solutions and, more particularly, in ink formulations comprising other chemicals and ingredients, extended agitation and aging periods are necessary before proper viscosity and dispersion can be attained.
For the above reasons, as stated, ink manufacturers have searched for a simple, fast and effective way of mixing anti-abrasion additives into ink systems. Because of this search, some commercial products are used by ink manufacturers as pourable liquid "concentrates". Such additives, in liquid form for inks and other compositions, usually involve taking the wax sold by a anti-abrasion wax manufacturing company and preparing, at the ink manufacturing operation by the ink manufacturer, a pre-mix liquid mixture or blend of the anti-abrasion wax and the ink vehicle being used to incorporate into the ink formulation.
Commercial anti-rub wax additives available in the marketplace include Protech 120, sold by Carroll Scientific, Inc. which is described as an 83% active compound containing some form of DuPont virgin Teflon.RTM. and a synthetic wax blend, with a petroleum distillate vehicle. Lawter International sells an anti-rub hard wax ink additive product, designated Lawter SA- 1021, which comprises a phenolic resin, some type of polytetrafluoroethylene, and a petroleum oil. It is also believed that commercial anti-rub wax additives containing polytetrafluoroethylene may have been sold in the past which may have also contained small amounts of some type of polyalphaolefins.
A number of prior art patents describe anti-abrasion additives for ink formulations and the use of polytetrafluoroethylene.
In non-ink applications, U.S. Pat. No. 5,159,019 describes the use of polytetrafluoroethylene in a resin mixture to provide abrasion resistance to plastic materials which are injection molded. U.S. Pat. No.4,096,207 shows the use of polytetrafluoroethylene to improve the abrasion resistance of elastomers which are in dynamic contact with metals.
U.S. Pat. No. 5,024,700 describes the use of triethanolamine as an ink additive, which among other properties, is described as providing improved rub resistance to oil and resin-based ink compositions, and as particularly useful for newspaper printing applications in this regard.
In the ink area, U.S. Pat. No. 3,843,570 describes a porous material comprising polytetrafluoroethylene obtained by polymerizing a monomer capable of forming a resin and discloses that the material is suitable with inks. U.S. Pat. No. 5,158,606 describes a printing ink composition with a high degree of rub-off resistance comprising a) a dispersion of a pigment in a vehicle containing an oil and b) polymer latex emulsified in said dispersion. The patent further discloses that where cost is not of paramount concern, a polytetrafluoroethylene wax can be added to the ink composition. Typically the polytetrafluoroethylene wax discussed comprises about 40 to 60 weight percent of polytetrafluoroethylene in a petrolatum base. Petrolatums are mineral oils or mineral jellies.